Tonight marks the summer solstice, the midpoint of summer (and what you’ll hear many people mistakenly call "the first day of summer"). The exact moment of the solstice occurs at 05:45 on June 21, but that’s June 20th in my part of the US (11:45 p.m. for me in Mountain time).

What does this mean, exactly? Well, say you were to go outside every day and map the path of the Sun across the sky. It would make an arc, of course. If you were to note the height above the horizon where the Sun reaches the top of that arc, and continue to note it every day for a year, you’d see that at the summer solstice that apex is highest above the horizon and at the winter solstice it’s at its lowest (southern hemispherites: swap those descriptions… and in reality it’s a bit more complicated than this, I know, but this is close enough).

This change in the height of the Sun’s path is because the Earth is tilted on its axis with respect to the plane of its orbit around the Sun. If you are so literal as to actually go out and measure the Sun’s path on the sky, you’ll note that starting today and going on for the next six months, the Sun will be lower and lower at local noon. When we reach the winter solstice on December 21st, the process will reverse, and off we go again.

So enjoy it now! For those of us north of the Equator, it means long days and short nights. As an astronomer that’s something of a bummer, but then as a blogger I hardly ever go outside anyway. Except, of course, to buy eggs and stand them on end.

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In Texas we do seasons a little different. There is Cold (or its more colloquial name of Close the Fridge Door You Dang Canadians, and Turn Off That Wind), followed by Hot (Satan vacations to get a break from the heat), Unbearably Hot (the longest season, Satan leaves because its too hot), and finally Thank [insert diety here] Its Not Unbearably Hot Anymore. You can tell this last season by all the leaves that are on the ground after finally exploding into flame. This used to be called Fall.

All of these seasons can overlap at any time (meaning it can be 100 in December or 50 in July), have no real pattern, and don’t seem to care about axis tilts, celestial equators, equinoxes (equinoxi?) or solsticeses.

I really need to find a new place to live: 72 degrees all the time, low humidity, and not too windy. Suggestions are appreciated!

I disagree with the “bad seasons” idea. Seasons are first and foremost climatic; the concept exists because the expected weather at various times of year have (and still do, to a lesser extent) determined what people have to do to survive. Where I’m sitting, at 3:00 Pacific time, we’re still having spring weather… and we usually are at the summer solstice.

If you want to talk about intensity of insolation, I’m on board. If you want to talk about the meaning of the word “seasons,” this is bad bad astronomy.

Hi all
Sorry to hijack this thread, but I thought you’ll find this interesting, and couldn’t find a better way.http://www.niburu.nl/index.php?articleID=21129
Appeared on some websites, to me it looks like some UFO believer made this up, and I don’t believe a bit of it, but I’m not an expert.

While I think Phil’s idea of what the seasons should be is correct (and certainly agrees with what we used to call the solstices in English — Midsummer and Midwinter,) the current official seasons of summer and winter do in fact start on the respective solstice and end on the corresponding equinox. All considering the seasons properly will get you is strange looks.

To milk this a little, it also happens to be my birthday. The other day, I mentioned the new age lady friend I knew years ago who thought I must have enormous woo-woo powers because I was born on midsummer day in Salisbury (which she knew only as the approximate site of Stonehenge). She was disappointed to no end to learn that I was a skeptic and did not believe in such things.
It was a short-lived relationship.

Lockwood I agree with you. Perhaps as a first order approximation if you ignore the effect of the Earth itself, then the solstices and equinoxes should be the midpoints of the seasons. However a second order approximation will take into account the insulating effect of the atmosphere, and the delayed heating of the air, the water, and the ground. This results in “the lag of the seasons” and is why meteorologists have labeled the seasons as starting at the solstices and equinoxes instead.

I was just in Norway where the sun doesn’t set during the summer solstice. The midnight sun is closer to the horizon than the midday sun (if you can call those times of day ‘midnight’ and ‘midday’) but that’s about it. I’m glad I was there around the summer and not the winter solstice.

Zandperl has it pretty darn close, I think. Weather guys have winter starting before the solstice. Wish I could remember what month they consider the start of winter, but I’m too lazy to look it up right now. Must recover from tour of wineries …

This change in the height of the Sun’s path is because the Earth is tilted on its axis with respect to the plane of its orbit around the Sun. If you are so literal as to actually go out and measure the Sun’s path on the sky, you’ll note that starting today and going on for the next six months, the Sun will be lower and lower at local noon. When we reach the winter solstice on December 21st, the process will reverse, and off we go again.

This is known in astronomy as the analemma (no juvenile jokes, please!). It is a curve representing the angular offset of a celestial body (usually the Sun) from its mean position on the celestial sphere as viewed from another celestial body (usually the Earth). For instance, knowing that Earth’s average solar day is almost exactly 24 hours, an analemma can be traced by plotting the position of the Sun as viewed from a fixed position on Earth at the same time every day for an entire year. The resulting curve resembles a figure of eight. This curve is commonly printed on globes. It is possible, though challenging, to ‘photograph’ the analemma, by leaving the camera in a fixed position for an entire year and snapping images on 24-hour intervals (or some multiple thereof).

I’ve always tried to claim the solstices (and equinoxes) as the mid-points of seasons, because of obvious astronomical arrangements. But then I’m met with arguments of “Then why does the calendar say this is the first day?” or “If Dec. 21 is the mid-point of winter why is the worst of it in February?”

Btw, Phil, yesterday I was browsing through some of your older entries at the old BA site, and thought that I’d leave some questions at the Mad Scientist Network. Unfortunately, the links don’t work anymore. Um, maybe the old BA sidebar link needs some updating. It gives a Page Load Error in my Firefox. If I guess correctly, this is where they are now:

All I know is that here in Alachua, Florida, at 12:30 AM local time, it is 82 degrees and 90% humidity.
The situation is not going to improve for several months, but it also has been nearly this bad for a month or so.

Lockwood is of course correct about the usual (cultural and thus practical) definition of seasons and Phil is once again wrong (not so surprisingly, by now). Of course, if you make the approximation that the earth HAS NO OCEANS, then Phil is closer to being right.

Here in Finland (and in other Nordic countries as well, I think) everyone thinks of the summer solstice as the midpoint of summer. There just no-one who thinks of it as the beginning of summer. There are actually a lot of “Mid-Summer fests” around this time.

Yes, the hottest part of the summer is usually still ahead, but so what? The hottest period can vary a lot. For example, where I live, the hottest days were before the summer solstice last year.

When the Sun is at its highest in the northern hemisphere, it’s the middle of summer here. It’s very clear-cut and doesn’t vary from year to year (like the hottest or coldest part of the season).

This is because of thermal inertia of the Earth’s oceans. Water has a large specific heat capacity of 4186 Joules/kg/K, and, just like water in your kettle, it takes a while to heat up and a while to cool down again.

According to Wikipedia on seasonal reckoning, meteorological seasons are reckoned by temperature, with summer being the hottest quarter of the year and winter the coldest quarter of the year. Using this reckoning, the Roman calendar began the year and the spring season on the first of March, with each season occupying three months. In 1780 the Societas Meteorologica Palatina, an early international organization for meteorology, defined seasons as groupings of three whole months. Ever since, professional meteorologists everywhere have used this definition. So, in meteorology for the Northern hemisphere: spring begins on 1 March, summer on 1 June, autumn on 1 September, and winter on 1 December.

In astronomical reckoning, the solstices and equinoxes ought to be the middle of the respective seasons, but, because of thermal lag, regions with a continental climate often consider these four dates to be the start of the seasons as in the diagram below, with the cross-quarter days considered seasonal midpoints. The length of these seasons is not uniform because of the elliptical orbit of the Earth and its different speeds along that orbit.

From the March equinox it takes 92.75 days until the June solstice, then 93.65 days until the September equinox, 89.85 days until the December solstice and finally 88.99 days until the March equinox.

Because of the differences in the Northern and Southern Hemispheres, it is no longer considered appropriate to use the northern-seasonal designations for the astronomical quarter days. The modern convention for them is: March Equinox; June Solstice; September Equinox; and December Solstice. The oceanic climate of the Southern Hemisphere produces a shorter temperature lag, so the start of each season is usually considered to be several weeks before the respective solstice or equinox in this hemisphere, in other countries with oceanic climates, and in cultures with Celtic roots.

#31 Evan asked: “Actually, why is the worst of winter always at the end?”

The Earth is always radiating heat into space, while at the same time absorbing heat from the Sun. The latter part of winter is colder, even though the days are longer, because the amount of heat the Sun provides even at that time is still not enough to overcome the loss of heat by radiation.

I found a bizarre thing the other day when I went to photograph the earliest sunrise – thanks to the analemma, the earliest sunrise is Jun 18th, so I figured that must be the longest day, right? Wrong – the latest sunset is actually Jun 24th, so on the 21st you get the longest day (difference between sunrise and sunset), even though that day has neither the earliest sunrise nor the latest sunset! Weird!

“at the summer solstice that apex is highest above the horizon and at the winter solstice it’s at its lowest (southern hemispherites: swap those descriptions… ”

GAAAAAAAAAHHHHHH! So many North Americans get this wrong! Phil, you get full points for realising that the southern hemisphere exists (unlike many people in the northern hemisphere). But let’s get something straight, for the benefit of everyone in the northern hemisphere; It is currently winter in the southern hemisphere. In the southern hemisphere, we call the (locally) warmest part of the year “summer”, and the coldest part “winter”. Crazy, huh? We also call that period when the sun is (locally) visible above the horizon “day” and the period when it’s hidden below the horizon “night”. Day and night vary depending on where you are on the Earth’s surface. Why should the naming of the seasons be any different? And why does nobody I talk to in North America get this concept?

Lockwood (37): I make a point in the linked article that defining seasons climactically is silly, since different places have different climates. In that case, why define them at all? In reality, having any hard and fast definition of seasons is rather silly, but if we’re going to do it, it should at least be somewhat logical.When people say “Today is the first day of summer” how is that any more right than what I am saying?

And oh, coolstar (#38) is back. I guess you didn’t see the followup comment I made to your incorrect and insulting assertions in the Star Trek review thread. Why do you feel the need to be so hostile?

The word solstice implies that the sun “stops”. I have been watching the sun setting along the horizon all 2009 and it was moving very rapidly northward in March around the equinox, but in recent weeks, it sets about the same place each night, thus “solstice”. Watch that sometime and it’ll be obvious.

Stand an egg on its end????
I thought you were supposed to be able to stand on an e….
Nevermind. I’ve got a mess to clean up.

But seriously, folks, here in the Garden of Eden that Phil abandoned (the one with all the wineries) we seeem to have the rainy season, the dry season, and that month to six weeks in August and September when it’s suddenly so blast oven hot that you’re afraid to open a door. (But it does pump up the sugars in those grapes!)

I didn’t get to see the sun today. It was cloudy and rainy all day. Stupid Japanese rainy season. But if I did see it at its highest point, it would have been at about 78 degrees above the horizon. It’s nearly overhead, and it’s strange walking on my own shadow.

It may be the mid-point of summer, but it’s more like the beginning of summer weather.

And this week, it’ll be 30 degrees C, cloudy, rainy and humid. Woo! Rainy season! Can’t wait for July and August with 32-35 degrees C, sunny, sunny and humid.

Yes, the seasons are opposite in the opposing hemispheres. Given that the seasons are caused by the Earth’s axial tilt, if one hemisphere is leaning towards the Sun, the other is leaning away.

As for temperatures, here in Canberra it’s already been cold. We’re away from the coast, so our summers are hotter and winters colder than the coastal cities. One day a couple of weeks ago we had a maximum temperature of 3 degrees C, the coldest day Canberra has had in more than 40 years.

When I worked for the Meteorological Service of New Zealand summer was defined as December, January and February, the reasoning being that the weather lagged behind the sun by several weeks. The other seasons followed with three months each. And of course it is Autumn, not this weird Fall stuff.

Phil (#48) says: ” I specifically say here that I am avoiding using weather in my reasoning.” OK, so let’s avoid referring to “fusion” when reasoning about stars. And the “different places have different climates” argument seems more than a little facile. Yes, Churchill, Manitoba has a different climate than Key West, Florida, but I’d be willing to bet that the climate is warmer in both places from June 21 to Sept. 21 than it is from ~April 6 to ~August 6. Another way of putting it is that August 6 to Sept. 21 is much more “summery” (sorry, another cultural reference that isn’t defined in astronomical or physical terms) than is the period from April 6 to June 21 for the vast bulk of inhabited extratropical areas in the northern hemisphere. Within the tropics, of course, “the seasons” aren’t a terribly useful concept; climate is much more contingent on regional geography than on the sun’s position in the sky. I didn’t bother getting into the heat inertia issue; I’m assuming that’s evident.

Phil, I can relate to your desire to nail things down, and your tendency to look for astronomical nails. Many of my physics friends tend to look at things the same way, and I tend to try to rationalize ways in which geology is the root cause of everything on earth. There is some truth and value in these endeavors, but to single-handedly declare that nearly everyone else is “wrong”, and a few astronomy nerds are “right”, with respect to what I think we agree is a culturally-based word, is at best silly. At worst, it’s heavy handed overreaching, and it’s the kind of thing that makes many people hostile to science.

Looking back, this seems to have a sterner tone than I’d prefer, over an issue that (again, I think we agree) is pretty trivial. So. Here are my suggestions for clarifying and physically defining common cultural concepts with an Astronomical and Physical Approach:

*Colors will no longer be named; we will teach people to refer to them by their frequencies. So, for example, “yellow” will henceforth be called “589 nm.” This has an added benefit in that people may come to comprehend that so called “microwaves” (which will now be called “0.1 to 10 cm”) are actually much less energetic or “dangerous” than visible light.

*ALL astronomical bodies that do not sustain fusion will be referred to as “STAR FAILs!” Let’s put this silly planet-plutoid-dwarf planet issue behind us for once and for all.

*The periodic table needs clarification too; it just keeps getting more and more cluttered:
1-Hydrogen; 2-Helium; 3- Metal. This will allow even kindergartners to memorize the entire thing.

*All physical entities will be referred to by their masses and appropriate stoichiometric chemical formulae. Care must be taken to calculate the molar proportions rather than mass proportions. Living entities should probably be designated as “O” for organic, 15 (see below). Non-living matter resulting from the death of a once-living entity will be likewise be distinguished with a “16” notation, for “post organic.” Using myself as a simple example, I should henceforth be addressed as (roughly) 100kg H10M6(15). Post mortem, I will be recalled by the same designation, but my corpus will be referred to in the present tense as 100kg H10M6(16)

*Musical Tempos will be redefined in terms of a range of pulsars. I have provided the groundwork for this conversion by finding the periods of three well-known examples, but I leave it to others more musically and astronomically knowlegeable to fill out the list and match them to corresponding passages of music. The notation in sheet music and scholarly research should use the appropriate astronomical designations (in parentheses below), rather than their common English names:
Crab Pulsar 0.033403347 s (PSR B0531+21)
Vela Pulsar 0.089298530 s (PSR B0833-45 or PSR J0835-4510) (Phil, why does this object have two designations?)
Vulpecula Pulsar 0.144457105 s (PSR B1937+21, sometimes written as PSR B1937+214) (!!!! Again? This isn’t science!)

*Musical notes will henceforth be designated by frequency (rather than by wavelength, to keep music distinct from light). Who was the dingbat that used letters, which aren’t defined physically, to describe music, which is first and foremost a physical phenomenon of both Stars and STAR FAIL’s! (the latter provided they have atmospheres of H, He, and/or M)? So, for example, “middle C” will now be referred to as “261.626 Hz.”

*Speaking of letters, this system is entirely culturally-based and needs to be brought up to tight, Mathematical Standards, worthy of being described as “Science.” Here’s my suggestion: each letter will act as an equivalent digit in a base-26 numerical system. So “and” represents 1*676 + 14*26 + 4 (base 10, our “native,” cultural base. We’ll work on that cultural influence later), or 1044. 1044 has a variety of meanings, which can be represented by using sub- and superscripts (though not in the word processing utility I’m working on at the moment. 1044 can act as a conjuction, it can imply addition, and it is a logical operator. Converting the English language to its base 10 equivalent will effectively and logically convert all discussion in that language to a series of calculations- the accuracy and truthfulness of which can be simply and quickly tested with a mere calculator. No more spin zone. No more propaganda from the anti-science and science illiterate. The lies and avoidance of truth will no longer be possible! Puntuation is currently an unresolved problem, but enormous strides forward are expected from research currently underway.

2. James:
Ah, Texas, I remember it well(Houston, Plano, Austin and Wichita Falls). I still have this mental image of ice cloaking the tree in our front yard in Plano from its crown to the ground. Brrr!!!
Weather is one reason I really miss Calif. For that really nice range(72 F.) try about half way between Los Angeles and San Francisco, about 2 – 3 Km inland from Pacific Coast Highway,,,The temps are very mellow all year round.

For what it’s worth, the coldest part of winter where I live isn’t at the official end, in February (This condition is probably common on North America’s coastal plains, as witnessed by the very popular “Groundhog Day”, a traditional turning point of the seasons, marked on the calendar at February 2) It’s generally in January, at only a few weeks’ distance from the solstice. It’s also been cold since September. Similarly, the hottest days are not in Augest but in July, again only a few weeks from the solstice.

Naturally (since I don’t grow anything,) climate is nearly irrelevant to my actual lifestyle. If I’m going to quarter the year, grouping together the days with similar lengths actually makes a bit more sense.

@Lockwood: This isn’t science-vs-culture. As I pointed out, culture had it right in the first place. Before we called them solstices, english-speakers referred to the days as “midsummer” and “midwinter,” correctly noting their positions in the middle of the respective seasons.

I suspect it’s actually meteorology (a science, of sorts) that’s brought us to the pass where culture and astronomy find themselves arrayed together against the calendar.

Someone asked me at a party yesterday what the second longest day was, the day before or after the solstice. Thinking about what I’ve learned here, I told them that I thought it depended on the year, but I wanted to verify.

I am late to this thread so I don’t know if it’s been mentioned, but you can also track the shadow of a permanently standing object like a telephone pole or a chimney to note the changes in the sun’s position during the year. It’s a bit safer than staring at the sun to try to determine (and remember) its relative position in the sky.

I’ve done this by sticking a marker in the ground to mark the daily shadow of a tree. (and I also noticed that I was observing a natural sundial)

@JediBear- exactly: a different culture, in a different place and time, defined them differently. We don’t live there. We live here, in this culture. So for a minor splinter of this culture (us astronomy nerds) to unilaterally declare that the vast number who are not astronerds are “mistaken” is more than a little presumptuous. Perhaps an analogy would help clarify: this culture defines “Christmas” as December 25. It also has a mistaken belief that this date is the anniversary of the birth of a person called “Jesus Christ.” The fact that this is a mistaken belief does not change the date of Christmas. So, JediBear, yes it is science vs. culture. And as I perhaps haven’t said clearly enough, when science tries to dictate to culture about what it should believe- particularly about a matter that is so trivial- I don’t see any good coming as a result. As I did say in my previous comment (59), “There is some truth and value in these endeavors, but to single-handedly declare that nearly everyone else is “wrong”, and a few astronomy nerds are “right”, with respect to what I think we agree is a culturally-based word, is at best silly. At worst, it’s heavy handed overreaching, and it’s the kind of thing that makes many people hostile to science.”

If you want to treat it as a joke, then we’re in agreement. That’s what I was trying to get at in the latter part of the above post. However, if you see science as the final arbiter of what is right and wrong for a culture to do, believe, and celebrate, then you put yourself in the same position as religions, and you deserve the same disdain with which I hold them. Science is not about “truth,” whatever that means, it’s about evidence. The evidence is that you and Phil are dissatisfied with the dominant definition of seasons- and I’m not trying to criticize or denigrate that dissatifaction. The evidence is also that you are in a very distinct minority. All I’m trying to say is that defending your position with the cloak of SCIENCE, and announcing to the world “I’m right and all you poor sods are wrong,” is not going to convince people, and is potentially damaging to the general attitude toward science.

The issue of “seasons” is not what we’re discussing here. What we’re discussing is the proper use and role of science. If you want to turn science into a faith-based dictatorship that imposes arbitrary standards, based on accurate, repeatable, observations that, nevertheless, have no significant impact on the lives of most people, and that, sadly, most people don’t know or comprehend, that’s your right. It’s my right to point out that I think that’s a really, really bad idea.

Likewise, to argue that people in the English middle ages celebrated the solstice as “midsummer,” therefore they’re right, and the vast majority of modern citizens are wrong, seems a little ridiculous too. What do you and Phil think about wearing scarves around your mouths and noses to prevent breathing the bad air that causes the black plague and malaria (malaria literally means “bad air”)?

Yes. Fall begins in the latter part of the summer. Doesn’t that make sense? The seasons don’t just end and begin abruptly, it is a gradual transformation.

People who feel that the beginning of a season can be pinpointed to the same specific date every year on our calendar do not garden or are unaware of their surroundings. The seasons are different every single year. In the Northwestern US, the bulbs and cherry blossoms started to sprout in mid-January along with temps in the 50s F. And this is not due to global warming, it is a common occurrence in two to three year cycles.

The notion that the seasons begin on the solstices and equinoxes is based on popular culture and now erroneously emblazoned on our calendars. The calendar should read “Spring Equinox” rather than “Spring begins.”

@Lockwood So the “entire world,” including all authority at the time, namely, the Roman Catholic Church, believed that the Earth is flat. Only Copernicus and Galileo believed otherwise. So, we should have stuck with popular culture I guess? What you consider trivial, as in the definition of solstice or equinox, others find interesting. If Christians choose to celebrate Christmas on an erroneous date, that’s their prerogative. I choose to celebrate the solstices and equinoxes as simply solstices and equinoxes, not as the beginnings or endings of seasons. The summer solstice simply defines the solstice that occurs within summer.